Hydraulic damper with a hydraulic compression stop assembly

ABSTRACT

A hydraulic damper for a vehicle including a main tube. A first piston assembly is slideably disposed in the main tube and axially divides the main tube into a rebound chamber and a primary compression chamber. A hydraulic compression stop assembly is disposed in the primary compression chamber and includes a narrowed section extending between an open end and a closed end. A second piston assembly is slideably disposed in the narrowed section and is coupled with the first piston assembly. The second piston assembly has a piston tube that extends between an opened end and a shut end. A displaceable partition is slideably disposed in the piston tube. A first auxiliary compression chamber is defined between the partition and the closed end of the narrowed section. A second auxiliary compression chamber is defined between the partition and the shut end of the piston tube.

TECHNICAL FIELD

The present invention generally relates to a hydraulic damper for avehicle. More particularly, the present invention relates to a hydraulicdamper including a hydraulic compression stop assembly.

BACKGROUND OF THE INVENTION

It is known in the art for hydraulic dampers to include a hydrauliccompression stop assembly for generating an additional damping forceover a predefined section of the piston rod travel during a compressionstroke.

An example of such a hydraulic damper is disclosed in internationalpatent application publication no. WO2016146660 which discloses ahydraulic stop member comprising a cup-shaped body, which is adapted tobe mounted in a compression chamber. The cup-shaped body is open at itstop end facing towards the piston of the shock-absorber, and comprises aside wall and a bottom wall which define, along with the plunger, aworking chamber. The side wall and the bottom wall are made as separatepieces and are connected to each other by force-fitting. The side wallhas axial channels formed on its inner surface configured to allow thedamping fluid to flow axially out of the working chamber. Furthermore,the cup-shaped body has an annular passage, which is in fluidcommunication with the portion of the compression chamber underneath thebottom wall of the hydraulic stop member.

Another example of such a hydraulic damper is disclosed in internationalpatent application publication no. WO2016126776 which discloses a shockabsorber having a hydraulic compression stop including a piston and asleeve. The sleeve has an open end for receiving the piston and a flowgroove that extends longitudinally along an inner surface of the sleeve.

Although hydraulic compression stop assemblies of this kind provideversatile tuning opportunities for shaping damping force characteristicsat the very high velocities that may occur during the compression stroke(e.g., while a vehicle hits an obstacle), forces can increase rapidlyleading even to damage of the internal components of the damper.Accordingly, there is a need for improvements to hydraulic damperassemblies.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a hydraulic damperwith a hydraulic compression stop assembly which is efficient and simpleto manufacture and assemble, and which provides a limit to the maximumdamping force that can be generated by the hydraulic compression stopassembly.

Another object of the present invention is to provide a damper with ahydraulic compression stop assembly that does not require substantialmodifications of the remaining components of the damper and might beemployed as an add-on device in existing damper designs.

A hydraulic damper for a vehicle. The hydraulic damper includes a maintube extending about and along an axis and filled with a working fluid.The main tube has a first inner diameter. A first piston assembly isdisposed in the main tube and axially divides the main tube into arebound chamber and a primary compression chamber. The first piston isaxially moveable in a compression stroke and a rebound stroke togenerate a damping force. A hydraulic compression stop assembly isdisposed in the compression chamber. The hydraulic compression stopassembly includes a narrowed section disposed in the compression chamberof the main tube. The narrowed section extends between an open end and aclosed end and has a second inner diameter that is smaller than thefirst inner diameter of the main tube. A second piston assembly isslideably disposed in the narrowed section and is coupled with the firstpiston assembly for axially moving with the first piston assembly forgenerating an additional damping force during the compression stroke.The second piston assembly has a piston tube that extends between anopened end and a shut end, with the shut end disposed opposite theclosed end of the narrowed section. A displaceable partition isslideably disposed in the piston tube of the second piston assembly forproviding an additional damping force during the compression stroke. Thedisplaceable partition defines a first auxiliary compression chamberbetween the partition and the closed end of the narrowed section. Asecond auxiliary compression chamber is defined between the partitionand the shut end of the piston tube.

According to another aspect of the disclosure, the first and secondauxiliary compression chambers are fluid tightly separated by thepartition.

According to another aspect of the disclosure, the partition defines apressure surface facing the closed end of the narrowed section forproviding sliding movement of the partition during a buildup of pressurein the first auxiliary compression chamber against the pressure surface.

According to another aspect of the disclosure, a spring extends betweenthe shut end of the piston tube of the second piston assembly and thepartition to bias the partition toward the closed end of the narrowedsection.

According to another aspect of the disclosure, a check valve allowsfluid to pass from the first auxiliary chamber into the primarycompression chamber.

According to another aspect of the disclosure, the check valve includesleast one radial opening defined by the piston tube for beingselectively covered by the partition, and the check valve furtherincludes at least one axial groove fluidly connecting the radial openingand the first auxiliary chamber.

According to another aspect of the disclosure, the partition includes apin extending axially toward the closed end of the narrowed section foracting as a mechanical bumper during axial movement of the partition.

According to another aspect of the disclosure, a sleeve is disposed inthe first auxiliary chamber and coupled with the piston tube, and thepartition is at least partially received by the sleeve.

According to another aspect of the disclosure, the sleeve is threadedlyconnected to the piston tube.

According to another aspect of the disclosure, the narrowed section isan insert received by the main tube.

BRIEF DESCRIPTION OF THE DRAWINGS

Other advantages of the present invention will be readily appreciated,as the same becomes better understood by reference to the followingdetailed description when considered in connection with the accompanyingdrawings wherein:

FIG. 1 illustrates a perspective fragment view of a vehicle suspensioncomprising a damper according to the present invention;

FIG. 2 is a schematic cross-sectional view of an embodiment of atwin-tube damper according to the present invention with a first exampleembodiment of a hydraulic compression stop assembly;

FIG. 3a is a schematic cross-sectional view of a second exampleembodiment of a compression stop assembly in a rebounded position;

FIG. 3b is a schematic cross-sectional view of the second exampleembodiment of a compression stop assembly in a compressed position;

FIG. 4 is a schematic cross-sectional view of a third embodiment of ahydraulic compression stop assembly; and

FIG. 5 is an axonometric view of the hydraulic compression stop assemblyshown in FIG. 1 and FIG. 2.

DESCRIPTION OF THE ENABLING EMBODIMENT

Referring to the Figures, wherein like numerals indicate correspondingparts throughout the several views,

FIG. 1 schematically illustrates a fragment of an exemplary vehiclesuspension comprising the damper 1 of the present invention attached toa vehicle chassis 101 by means of a top mount 102 and a number of screws103 disposed on the periphery of an upper surface of the top mount 102.The top mount 102 is connected to a coil spring 104 and a piston rod 5of the damper 1. The tube 2 of the damper 1 is connected to a steeringknuckle 105 supporting a vehicle wheel 106.

FIG. 2 presents an embodiment of a twin-tube damper 1 according to thepresent invention. The damper 1 comprises an external tube 2 and a maintube 3, each extending about and along an axis A and filled with viscousworking liquid inside of which a movable piston assembly 4 attached to apiston rod 5 led outside the damper 1 through a sealed piston rod guide6 is disposed. The main tube 3 has a first inner diameter D1. The damper1 is also provided with a base valve assembly 7 fixed at the end of themain tube 3 opposite the rod guide 6. The piston assembly 4 makes asliding fit with the inner surface of the main tube 3 and divides thetube 3 into a rebound chamber 11 (between the piston assembly 4 and thepiston rod guide 6) and a primary compression chamber 12 (between thepiston assembly 4 and the base valve assembly 7). An additionalcompensation chamber 13 is located at the other side of the base valveassembly 7. The main piston assembly 4 is axially moveable in acompression stroke toward the piston based valve assembly 7 and arebound stroke toward the piston rod guide 6.

The piston assembly 4 is provided with compression 42 and rebound 41valve assemblies to control the flow of working liquid passing betweenthe rebound chamber 11 and the primary compression chamber 12 while thepiston assembly 4 is in motion along an axis A. Also the base valveassembly 7 is provided with rebound 71 and compression 72 valveassemblies to control the flow of working liquid passing between theadditional compensation chamber 13 and the primary compression chamber12, respectively, during rebound and compression stroke of the damper 1.As it is well known to those skilled in the art, the valve assemblies41, 42 and 71, 72 provide design parameters that may be used to shapedesired characteristic of the twin-tube damper 1.

The damper 1 is further provided with a hydraulic compression stopassembly 8 located in the primary compression chamber 12 to generate anadditional damping force at the end of the compression stroke e.g., inorder to avoid an abrupt stop of the piston assembly 4. The compressionstop assembly 8 comprises a narrowed section 81 and a second pistonassembly 83 apt to be slidably received in this narrowed section 81 togenerate an additional damping force at the end of the compressionstroke.

The narrowed section 81 has in the presented embodiments form of aninsert made of integrally moulded polyamide 6.6 forming a single pieceand disposed inside the damper 1 main tube 3 with a loose fit. Thenarrowed section 81 extends between an open end 109 and a closed end 111and has a second inner diameter D2 that is smaller than the first innerdiameter D1. At its closed end 111 the insert 81 is provided with acircumferential locking yoke 813 extending annularly about a half of theperimeter of the insert 81 and embracing a fixing member 82 press-fittedon the base valve assembly 7. The fixing member 82 is made of sinteredsteel and stabilises the axial position of the insert 81. The fixingmember 82 is also provided with a number of equiangularly spaced axialchannels 821 (cf. FIG. 5) enabling for a fluid communication between theprimary compression chamber 12 and the additional compensation chamber13 through the base valve assembly 7 during the compression and therebound stroke of the damper 1. Furthermore, as shown in FIG. 5, theinsert 81 is provided with five equiangularly spaced ribs 811 defining aplurality of slots 812 in between, which are delimited at the outside bythe internal surface of the main tube 3. The slots 812 also enable for aflow of the working liquid between the primary compression chamber 12and the additional compensation chamber 13 through the base valveassembly 7 during the compression and the rebound stroke of the damper1.

The second piston assembly 8 includes a piston tube 113 extendingbetween an opened end 115 and a shut end 117, with the shut end 117disposed opposite the open end 109 of the narrowed section 81. Athreaded opening 833 is defined at the shut end 117 which enablesthreaded of the assembly on an external thread of a threaded projection511 of a piston rod extender 51 fixed to the piston rod 5 so that thesecond piston assembly 83 is displaceable along with the main pistonassembly 4. The external diameter of the second piston assembly 83 issmaller than the first inner diameter D1 of the main tube 3 enabling fora free flow of working liquid while the second piston assembly 83 moveswithin the tube 3 and outside the region of the insert 81.

The compression stop assembly 8 further includes a partition 86 axiallyslideably disposed in the piston tube 113 to define an internal firstauxiliary compression chamber 84 between the partition 86 and the closedend 11 of the narrowed section 81, and a second auxiliary compressionchamber 85 between the partition 86 and the shut end 117 of the pistontube 113.

The reference numerals corresponding to the same functional elementsremain the same throughout the description with suffixes (a, b) added,where appropriate to distinguish particular embodiments of the pistonassembly 8 a and 8 b.

In the embodiments 8 and 8 a of the compression stop assembly, thepartition 86 comprises an annular seal 861 and fluid tightly separatesthe first auxiliary compression chamber 84 from the second auxiliarycompression chamber 85. Since the first auxiliary compression chamber 84is in an inactive state of the compression stop assembly 8 fluidlyconnected with the primary compression chamber 12, it is filed withviscous working liquid. However in the embodiments 8 and 8 a, the secondauxiliary compression chamber 85 is filed with air or other gaseousmedium under a predefined pressure, that should usually be higher thanatmospheric pressure.

The second piston assembly 83 further comprises a threaded fixing sleeve831 and a sealing ring 832 providing a sealing while the second pistonassembly 83 moves within the inner insert 81. The sleeve 831 is providedwith an external annular torque application surface enabling forscrewing the sleeve 831 inside the second piston assembly 83 by means ofa flat wrench. The fixing sleeve 831 holds a sealing ring 832 andprovides a retaining surface for the partition 86 which in an inactivestate of the stop assembly 8 is pushed towards the fixing sleeve 831 bythe pressure of the gas inside the second auxiliary compression chamber85.

When the second piston assembly 83 is disposed within the insert 81 andadvances further during the compression stroke of the damper 1, thepressure of the working liquid inside the first auxiliary compressionchamber 84, that acts on a predefined pressure surface B of thepartition 86, increases and after equalizing gas pressure inside thesecond auxiliary compression chamber 85 it will push the partition 86inside the second auxiliary compression chamber 85 enabling for workingliquid accumulation inside the second piston assembly 83 and thereforefor a smooth increase of the stop 8 reaction force. Obviously, as thediameter of the second piston assembly 83 is smaller than the internaldiameter of the insert 81, also the available volume beneath thepartition 86 that is available for working liquid is smaller than thecorresponding volume of the insert 81. As shown in FIG. 2 in an extremeposition of the compression stop 8, the first auxiliary compressionchamber 84 filed with working liquid is located not only within theinsert 81 but also extends inside the second piston assembly 83 formingan oil volume accumulator therein.

FIGS. 3 and 4 illustrate other exemplary embodiments of the compressionstop assemblies according to the present invention.

In an embodiment of the compression stop assembly 8a shown in FIG. 3 thepartition 86 is additionally provided with a cylindrical projection 862disposed slidably within the fixing sleeve 831. Therefore the partition86 is disposed slidably both within the second piston assembly 83, aswell as within the sleeve 831.

Furthermore the second piston assembly 83 comprises a number of checkvalves 87 in a form of radial openings opened at the outside of thesecond piston assembly 83 and at the inside normally covered by thepartition 86. Furthermore in this embodiment the cylindrical projection862 of the partition is provided with a number of equiangularly spacedaxial grooves 863 and also the fixing sleeve 831 is provided with anumber of equiangularly spaced axial grooves 834. When the partition 86is pushed inside the second auxiliary compression chamber 85, theopenings 87 and the grooves 863 and 834 enable for a restricted flow ofworking liquid from the first auxiliary compression chamber 84 of thehydraulic compression stop assembly 8 and the main primary compressionchamber 12 of the damper 1, while the partition 86 uncovers the openings87, as shown by a dashed arrow in FIG. 3 b.

An embodiment of the compression stop assembly 8b shown in FIG. 4comprises a coil spring 88 preloaded with a predefined pressure in thesecond auxiliary compression chamber 85 between the shut end 117 of thesecond piston assembly 83 and the partition 86 to bias the partition 86toward the closed end 111 of the narrowed section 81. The partition 86is also provided with a cylindrical projection 862 disposed slidablywithin the fixing sleeve 831 but in this embodiment only thiscylindrical projection 862 provides axial guidance for the partition 86within the sleeve 831. The sleeve 831 has an internal torque applicationsurface for a hex key.

As shown, the insert 81 is provided at its entry with five equiangularlyspaced grooves 814 extending longitudinally towards a closed end of thefirst auxiliary compression chamber 84 that allow the working liquid toflow out of and into the chamber 84 around the second piston assembly 83respectively during compression and rebound stroke. As thecross-sectional surface of the grooves 814 diminishes along theirlength, the damping force also increases. Furthermore the insert 81 isshaped at its entry to form a conical section 815 followed by acylindrical section 816. The conical section 815 guides the secondpiston assembly 83 upon its entry to the first compression chamber 85.Furthermore such a shaping along with the grooves 814 provide smoothbuilt-up of the damping force.

In this embodiment the predefined preload force F₀ of the spring 88establishes a neutral position of the partition 86, while the outerdiameter of the cylindrical projection 862 defines the adjustablepressure surface B upon which acts the pressure P in the first auxiliarycompression chamber 84 against the preload force F₀ of the spring.Therefore as soon as P·B≥F₀ the spring 88 will compress and thepartition 86 will be pushed inside the second auxiliary compressionchamber 85 with a reaction force linearly proportional to the deflectionof the spring 88. This embodiment is remarkably easy and economical tomanufacture. A low spring rate, which in this embodiment amounts about10 N/mm, provides slight and linear force progression.

In this embodiment, the projection 862 of the partition 861 is alsoprovided with an axial pin 864 apt to act as an additional mechanicalbumper if the reaction of the spring 88 induced by the pressure surfaceB of the projection 862 was insufficient.

The above embodiments of the present invention are merely exemplary. Thefigures are not necessarily to scale, and some features may beexaggerated or minimized. These and other factors however should not beconsidered as limiting the spirit of the invention, the intended scopeof protection of which is indicated in appended claims. Obviously, manymodifications and variations of the present invention are possible inlight of the above teachings and may be practiced otherwise than asspecifically described while within the scope of the appended claims.

What is claimed is:
 1. A hydraulic damper for a vehicle, comprising: amain tube extending about and along an axis and having a first innerdiameter and filed with working liquid; a first piston assembly disposedin said main tube and axially dividing said main tube into a reboundchamber and a primary compression chamber, and axially moveable in acompression stroke and a rebound stroke to generate a damping force; ahydraulic compression stop assembly disposed in said compressionchamber, said hydraulic compression stop assembly including: a narrowedsection disposed in said compression chamber of said main tube andextending between an open end and a closed end and having a second innerdiameter being smaller than said first inner diameter of said main tube;a second piston assembly slideably disposed in said narrowed section andcoupled with said first piston assembly for axially moving with saidfirst piston assembly for generating an additional damping force duringsaid compression stroke; said second piston assembly having a pistontube extending between an opened end and a shut end, with said shut enddisposed opposite said closed end of said narrowed section; and adisplaceable partition slideably disposed in said piston tube of saidsecond piston assembly for providing an additional damping force duringsaid compression stroke, said displaceable partition defining a firstauxiliary compression chamber between said partition and said closed endof said narrowed section, and a second auxiliary compression chamberbetween said partition and said shut end of said piston tube.
 2. Thehydraulic damper according to claim 1, wherein said first and secondauxiliary compression chambers are fluid tightly separated by saidpartition.
 3. The hydraulic damper according to claim 1, wherein saidpartition defines a pressure surface facing said closed end of saidnarrowed section providing sliding movement of said partition during abuildup of pressure in said first auxiliary compression chamber againstsaid pressure surface.
 4. The hydraulic damper according to claim 1,wherein a spring extends between said shut end of said second pistonassembly and said partition to bias said partition toward said closedend of said narrowed section.
 5. The hydraulic damper according to claim1, further including a check valve allowing fluid to pass from saidfirst auxiliary compression chamber into said primary compressionchamber.
 6. The hydraulic damper according to claim 5, wherein saidcheck valve includes at least one radial opening defined by said pistontube for being selectively covered by said partition, and wherein saidcheck valve further includes at least one axial groove fluidlyconnecting said radial opening and said first auxiliary compressionchamber.
 7. The hydraulic damper according to claim 1, wherein saidpartition includes a pin extending axially toward said closed end ofsaid narrowed section for acting as a mechanical bumper during axialmovement of said partition.
 8. The hydraulic damper according to claim1, wherein a sleeve is disposed in said first auxiliary compressionchamber and coupled with said piston tube, and wherein said partition isat least partially received by said sleeve.
 9. The hydraulic damperaccording to claim 8, wherein said sleeve is threadedly connected tosaid piston tube.
 10. The hydraulic damper according to claim 1, whereinsaid narrowed section is an insert received by said main tube.